This invention relates to a high performance multi-media communications cable utilizing paired or unpaired electrical conductors or optical fibers. More particularly, it relates to cables having a central core defining singular or plural individual pair channels. The communications cable has an interior core support-separator that defines a clearance through which conductors or optical fibers may be disposed.
Many communication systems utilize high performance cables normally having four pairs or more that typically consist of two twisted pairs transmitting data and two receiving data as well as the possibility of four or more pairs multiplexing in both directions. A twisted pair is a pair of conductors twisted about each other. A transmitting twisted pair and a receiving twisted pair often form a subgroup in a cable having four twisted pairs. High-speed data communications media in current usage includes pairs of wire twisted together to form a balanced transmission line. Optical fiber cables may include such twisted pairs or replace them altogether with optical transmission media (fiber optics).
When twisted pairs are closely placed, such as in a communications cable, electrical energy may be transferred from one pair of a cable to another. Energy transferred between conductor pairs is undesirable and referred to as crosstalk. The Telecommunications Industry Association and Electronics Industry Association have defined standards for crosstalk, including TIA/EIA-568A. The International Electrotechnical Commission has also defined standards for data communication cable crosstalk, including ISO/IEC 11801. One high-performance standard for 100 MHz cable is ISO/IEC 11801, Category 5. Additionally, more stringent standards are being implemented for higher frequency cables including Category 6 and Category 7, which includes frequencies of 200 and 600 MHz, respectively.
In conventional cable, each twisted pair of conductors for a cable has a specified distance between twists along the longitudinal direction. That distance is referred to as the pair lay. When adjacent twisted pairs have the same pair lay and/or twist direction, they tend to lie within a cable more closely spaced than when they have different pair lays and/or twist direction. Such close spacing increases the amount of undesirable crosstalk that occurs. Therefore, in many conventional cables, each twisted pair within the cable has a unique pair lay in order to increase the spacing between pairs and thereby to reduce the crosstalk between twisted pairs of a cable. Twist direction may also be varied. Along with varying pair lays and twist directions, individual solid metal or woven-metal air shields can be used to electromagnetically isolate pairs from each other or isolate the pairs from the cable jacket.
Shielded cable, although exhibiting better crosstalk isolation, is more difficult, time consuming and costly to manufacture, install, and terminate. Individually shielded pairs must generally be terminated using special tools, devices and techniques adapted for the job, also increasing cost and difficulty.
One popular cable type meeting the above specifications is Unshielded Twisted Pair (UTP) cable. Because it does not include shielded pairs, UTP is preferred by installers and others associated with wiring building premises, as it is easily installed and terminated. However, UTP fails to achieve superior crosstalk isolation such as required by the evolving higher frequency standards for, data and other state of the art transmission cable systems, even when varying pair lays are used.
Some cables have used supports in connection with twisted pairs. These cables, however, suggest using a standard xe2x80x9cXxe2x80x9d, or xe2x80x9c+xe2x80x9d shaped support, hereinafter both referred to as the xe2x80x9cXxe2x80x9d support. Protrusions may extend from the standard xe2x80x9cXxe2x80x9d support. The protrusions of these prior inventions have exhibited substantially parallel sides.
The document, U.S. Pat. No. 3,819,443, hereby incorporated by reference, describes a shielding member comprising laminated strips of metal and plastics material that are cut, bent, and assembled together to define radial branches on said member. It also describes a cable including a set of conductors arranged in pairs, said shielding member and an insulative outer sheath around the set of conductors. In this cable the shielding member with the radial branches compartmentalizes the interior of the cable. The various pairs of the cable are therefore separated from each other, but each is only partially shielded, which is not so effective as shielding around each pair and is not always satisfactory.
The solution to the problem of twisted pairs lying too closely together within a cable is embodied in three U.S. Pat. Nos. 6,150,612 to Prestolite, 5,952,615 to Filotex, and 5,969,295 to CommScope incorporated by reference herein, as well as an earlier similar design of a cable manufactured by Belden Wire and Cable Company as product number 1711A. The prongs or splines in the Belden cable provide superior crush resistance to the protrusions of the standard xe2x80x9cXxe2x80x9d support. The superior crush resistance better preserves the geometry of the pairs relatives to each other and of the pairs relative to the other parts of the cables such as the shield. In addition, the prongs or splines in this invention preferably have a pointed or slightly rounded apex top which easily accommodates an overall shield. These cables include four or more twisted pair media radially disposed about a xe2x80x9c+xe2x80x9d-shaped core. Each twisted pair nests between two fins of the xe2x80x9c+xe2x80x9d-shaped core, being separated from adjacent twisted pairs by the core. This helps reduce and stabilize crosstalk between the twisted pair media. U.S. Pat. No. 5,789,711 to Belden describes a xe2x80x9cstarxe2x80x9d separator that accomplishes much of what has been described above and is also herein incorporated by reference.
However, these core types can add substantial cost to the cable, as well as material which forms a potential fire hazard, as explained below, while achieving a crosstalk reduction of typically 3 dB or more. This crosstalk value is based on a cable comprised of a fluorinated ethylene-propylene (FEP) conductors with PVC jackets as well as cables constructed of FEP jackets with FEP insulated conductors. Cables where no separation between pairs exist will exhibit smaller crosstalk values. When pairs are allowed to shift based on xe2x80x9cfree spacexe2x80x9d within the confines of the cable jacket, the fact that the pairs may xe2x80x9cfloatxe2x80x9d within a free space can reduce overall attenuation values due to the ability to use a larger conductor to maintain 100 ohm impedance. The trade-off with allowing the pairs to float is that the pair of conductors tend to separate slightly and randomly. This undesirable separation contributes to increased structural return loss (SRL) and more variation in impedance. One method to overcome this undesirable trait is to twist the conductor pairs with a very tight lay. This method has been proven impractical because such tight lays are expensive and greatly limits the cable manufacturer""s throughput (yield). An improvement included by the present invention to structural return loss and improved attenuation is to provide grooves within channels for conductor pairs such that the pairs are fixedly adhered to the walls of these grooves or at least forced within a confined space to prevent floating simply by geometric configuration.
In building designs, many precautions are taken to resist the spread of flame and the generation of and spread of smoke throughout a building in case of an outbreak of fire. Clearly, the cable is designed to protect against loss of life and also minimize the costs of a fire due to the destruction of electrical and other equipment. Therefore, wires and cables for building installations are required to comply with the various flammability requirements of the National Electrical Code (NEC) in the U.S. as well as International Electrotechnical Commission (EIC) and/or the Canadian Electrical Code (CEC).
Cables intended for installation in the air handling spaces (i.e. plenums, ducts, etc.) of buildings are specifically required by NEC/CEC/IEC to pass the flame test specified by Underwriters Laboratories Inc. (UL), UL-910, or its Canadian Standards Association (CSA) equivalent, the FT6. The UL-910 and the FT6 represent the top of the fire rating hierarchy established by the NEC and CEC respectively. Also important are the UL 1666 Riser test and the IEC 60332-3C and D flammability criteria. Cables possessing these ratings, generically known as xe2x80x9cplenumxe2x80x9d or xe2x80x9cplenum ratedxe2x80x9d or xe2x80x9criserxe2x80x9d or xe2x80x9criser ratedxe2x80x9d, may be substituted for cables having a lower rating (i.e. CMR, CM, CMX, FT4, FTI or their equivalents), while lower rated cables may not be used where plenum or riser rated cables are required.
Cables conforming to NEC/CEC/IEC requirements are characterized as possessing superior resistance to ignitability, greater resistant to contribute to flame spread and generate lower levels of smoke during fires than cables having lower fire ratings. Often these properties can be anticipated by the use of measuring a Limiting Oxygen Index (LOI) for specific materials used to construct the cable. Conventional designs of data grade telecommunication cable for installations in plenum chambers have a low smoke generating jacket material, e.g. of a specially filled PVC formulation or a fluoropolymer material, surrounding a core of twisted conductor pairs, each conductor individually insulated with a fluorinated insulation layer. Cable produced as described above satisfies recognized plenum test requirements such as the xe2x80x9cpeak smokexe2x80x9d and xe2x80x9caverage smokexe2x80x9d requirements of the Underwriters Laboratories, Inc., UL910 Steiner tunnel test and/or Canadian Standards Association CSA-FT6 (Plenum Flame Test) while also achieving desired electrical performance in accordance with EIA/TIA-568A for high frequency signal transmission.
While the above described conventional cable, including the Belden 1711A cable design, due in part to their use of fluorinated polymers, meets all of the above design criteria, the use of fluorinated polymers is extremely expensive and may account for up to 60% of the cost of a cable designed for plenum usage. The solid core of these communications cables contribute a large volume of fuel to a potential cable fire. Forming the core of a fire resistant material, such as with FEP, is very costly due to the volume of material used in the core, but it should help reduce flame spread over the 20 minute test period.
Solid flame retardant/smoke suppressed polyolefins may also be used in connection with fluorinated polymers. Commercially available solid flame retardant/smoke suppressed polyolefin compounds all possess dielectric properties inferior to that of FEP and similar fluorinated polymers. In addition, they also exhibit inferior resistance to burning and generally produce more smoke than FEP under burning conditions.
A high performance communications data cable utilizing twisted pair technology must meet exacting specification with regard to data speed, electrical,as well as flammability and smoke characteristics. The electrical characteristics include specifically the ability to control impedance, near-end cross-talk (NEXT), ACR (attenuation cross-talk ratio) and shield transfer impedance. A method used for twisted pair data cables that has been tried to meet the electrical characteristics, such as controlled NEXT, is by utilizing individually shielded twisted pairs (ISTP). These shields insulate each pair from NEXT. Data cables have also used very complex lay techniques to cancel E and B (electric and magnetic fields ) to control NEXT. In addition, previously manufactured data cables have been designed to meet ACR requirements by utilizing very low dielectric constant insulation materials. Use of the above techniques to control electrical characteristics have inherent problems that have lead to various cable methods and designs to overcome these problems. Current designs must also meet the UL 910 flame and smoke criteria using both fluorinated and non-fluorinated jackets as well as fluorinated and non-fluorinated insulation materials for the conductors of these cable constructions. In Europe, the trend continues to be use of halogen free insulation for all components, which also must meet stringent flammability regulations.
Individual shielding is costly and complex to process. Individual shielding is highly susceptible to geometric instability during processing and use. In addition, the ground plane of individual shields, 360xc2x0 in ISTP""sxe2x80x94individually shielded twisted pairs is also an expensive process. Lay techniques and the associated multi-shaped anvils of the present invention to achieve such lay geometries are also complex, costly and susceptible to instability during processing and use. Another problem with many data cables is their susceptibility to deformation during manufacture and use. Deformation of the cable geometry, such as the shield, also potentially severely reduces the electrical and optical consistency.
Optical fiber cables exhibits a separate set of needs that include weight reduction (of the overall cable), optical functionality without change in optical properties and mechanical integrity to prevent damage to glass fibers. For multi-media cable, i.e. cable that contains both metal conductors and optical fibers, the set of criteria is often incompatible. The use of the present invention, however, renders these often divergent set of criteria compatible. Specifically, optical fibers must have sufficient volume in which the buffering and jacketing plenum materials (FEP and the like) covering the inner glass fibers can expand and contract over a broad temperature range without restriction, for example xe2x88x9240 C to 80 C experienced during shipping. It has been shown by Grune, et. al., among others, that cyclical compression and expansion directly contacting the buffered glass fiber causes excess attenuation light loss (as measured in dB) in the glass fiber. The design of the present invention allows for designation and placement of optical fibers in clearance channels provided by the support-separator, having multi-anvil shaped profiles. It would also be possible to place both glass fiber and metal conductors in the same designated clearance channel if such a design is required. In either case the forced spacing and separation from the cable jacket (or absence of a cable jacket) would eliminate the undesirable set of cyclical forces that cause excess attenuation light loss. In addition, fragile optical fibers are susceptible to mechanical damage without crush resistant members (in addition to conventional jacketing). The present invention also addresses this problem.
The need to improve the cable design, reduce costs, and improve both flammability and electrical properties continues to exist.
This invention provides a lower cost communications cable exhibiting improved electrical, flammability, and optionally, optical properties. The cable has an interior support extending along the longitudinal length of the communications cable. The interior support has a central region extending along the longitudinal length of the interior support. In the preferred configuration, the cable includes a geometrically symmetrical core support-separator with a plurality of either solid or foamed anvil-shaped sections that extend radially outward from the central region along the longitudinal or axial length of the cable""s central region. The core support-separator is optionally foamed and has an optional hollow center. Each section is adjacent to each other with a minimum of two adjacent anvil-shaped sections. The anvil-shaped sections of the core support-separator may be helixed as the core extends along the length of the communications cable. Each of the adjacent anvil-shaped sections defines a clearance which extends along the longitudinal length of the multi-anvil shaped core support-separator. The clearance provides a channel for each of the conductors/optical fibers or conductor pairs used within the cable. The clearance channels formed by the multi-anvil shaped core support-separator extend along the same length of the central portion. The channels are either semi-circular or fully circular shaped cross-sections with completely closed surfaces in the radial direction toward the center portion of the core and optionally opened or closed surfaces at the outer radial portion of the same core. Adjacent channels are separated from each other to provide a chamber for at least a pair of conductors or an optical fiber or optical fibers.
The anvil-shaped core support-separator of this invention provides a superior crush resistance to the protrusions of the standard xe2x80x9cXxe2x80x9d or other similar supports. The superior crush resistance is obtained by the arch-like design of each clearance channel providing additional support to the outer section of the cable. The anvil-shaped core better preserves the geometry of the pairs relative to each other and of the pairs relative to the other parts of the cables, such as the possible use of a shield or optical fibers. In addition, the anvil-shape provides an exterior surface that essentially establishes the desired roundness for cable manufacturers. The exterior roundness ensures ease of die development and eventual extrusion. The rounded surface of the core also allows for easy accommodation of an overall external shield.
According to one embodiment, the cable includes a plurality of transmission media with metal and/or optical conductors that are individually disposed; and an optional outer jacket maintaining the plurality of data transmission media in proper position with respect to the core. The core is comprised of a support-separator having a multi-anvil shaped profile that defines a clearance to maintain a spacing between transmission media or transmission media pairs in the finished cable. The core may be formed of a conductive or insulative material to further reduce crosstalk, impedance and attenuation.
Accordingly, the present invention provides for a communications cable, with a multi-anvil shaped support-separator, that meets the exacting specifications of high performance data cables and/or fiber optics or the possibility of including both transmission media in one cable, has a superior resistance to deformation during manufacturing and use, allows for control of near-end cross-talk, controls electrical instability due to shielding, is capable of 200 and 600 MHz (Categories 6 and 7) transmission with a positive attenuation to cross-talk ratio (ACR ratio) of typically 3 to 10 dB.
Moreover, the present invention provides a separator so that the jacket material (which normally has inferior electrical properties as compared with the conductor material) is actually pushed away from the electrical conductor, thus acting to again improve electrical performance (ACR, etc.) over the life of the use of the cable. The anvil-shaped separator, by simple geometric considerations is also superior to the xe2x80x9cXxe2x80x9d type separator in that it increases the physical distance between the conductor pairs within the same cable configuration, as shown in FIGS. 2 and 3.
Additionally, it has been known that the conductor pair may actually have physical or chemical bonds that allow for the pair to remain intimately bound along the length of the cavity in which they lie. The present invention describes a means by which the conductor pairs are adhered to or forced along the cavity walls by the use of grooves. This again increases the distance, thereby increasing the volume of air or other dielectrically superior medium between conductors in separate cavities. As discussed above, spacing between pairs, spacing away from jackets, and balanced spacing all have an effect on final electrical cable performance.
It is an object of the invention to provide a data/multi-media cable that has a specially designed interior support that accommodates conductors with a variety of AWG""s, impedances, improved crush resistance, controlled NEXT, controlled electrical instability due to shielding, increased breaking strength, and allows the conductors, such as twisted pairs, to be spaced in a manner to achieve positive ACR ratios.
It is still another object of the invention to provide a cable that does not require individual shielding and that allows for the precise spacing of conductors such as twisted pairs and/or fiber optics with relative ease. In the present invention, the cable would include individual glass fibers as well as conventional metal conductors as the transmission medium that would be either together or separated in clearance channel chambers provided by the anvil-shaped sections of the core support-separator.
Another embodiment of the invention includes having a multi-anvil shaped core support-separator with a central region that is either solid or partially solid. This includes the use of a foamed core and/or the use of a hollow center of the core, which in both cases significantly reduces the material required along the length of the finished cable. The effect of foaming and/or producing a support-separator with a hollow center portion should result in improved flammability of the overall cable by reducing the amount of material available as fuel for the UL 910 test, improved electrical properties for the individual non-optical conductors, and reduction of weight of the overall cable.
Another embodiment includes fully opened surface sections defining the core clearance channels which extend along the longitudinal length of the multi-anvil shaped core support-separator. This clearance provides half-circular channel walls for each of the conductors/optical fibers or conductor pairs used within the cable. A second version of this embodiment includes a semi-closed or semi-opened surface section defining the same core clearance channel walls. These channel walls would be semi-circular to the point that at least 200 degrees of the potential 360 degree wall enclosure exists. Typically, these channels walls would include and opening of 0.005 inches to 0.011 inches wide. A third version of this embodiment includes either a fully closed channel or an almost fully closed channel of the anvil-shaped core support-separator such that this version could include the use of a xe2x80x9cflap-topxe2x80x9d initially providing an opening for insertion of conductors or fibers and thereafter providing a covering for these same conductors or fibers in the same channel. The flap-top closure can be accomplished by a number of manufacturing methods including heat sealing during extrusion of the finished cable product. Other methods include a press-fit design, taping of the full assembly, or even a thin skin extrusion that would cover a portion of the multi-anvil shaped separator. All such designs could be substituted either in-lieu of a separate cable jacket or with a cable jacket, depending on the final property requirements.
Yet another embodiment of the invention allows for interior corrugated clearance channels provided by the anvil-shaped sections of the core support-separator. This corrugated internal section has internal axial grooves that allow for separation of conductor pairs from each other or even separation of single conductors from each other as well as separation of optical conductors from conventional metal conductors.
Alternatively, the edges of said grooves may allow for separation thus providing a method for uniformly locating or spacing the conductor pairs with respect to the channel walls instead of allowing for random floating of the conductor pairs.
Each groove can accommodate at least one twisted pair. In some instances, it may be beneficial to keep the two conductors in intimate contact with each other by providing grooves that ensure that the pairs are forced to contact a portion of the wall of the clearance channels. The interior support provides needed structural stability during manufacture and use. The grooves also improve NEXT control by allowing for the easy spacing of the twisted pairs. The easy spacing lessens the need for complex and hard to control lay procedures and individual shielding. Other significant advantageous results such as: improved impedance determination because of the ability to precisely place twisted pairs: the ability to meet a positive ACR value from twisted pair to twisted pair with a cable that is no larger than an ISTP cable; and an interior support which allows for a variety of twisted pair and optical fiber dimensions.
Yet another related embodiment includes the use of an exterior corrugated or convoluted design such that the outer surface of the support-separator has external radial grooves along the longitudinal length of the cable. This exterior surface can itself function as a jacket if the fully closed anvil-shaped version of the invention as described above is utilized. Additionally, the jacket may have a corrugated, smooth or ribbed surface depending on the nature of the installation requirements. In raceways or plenum areas that are new and no previous wire or cable has been installed, the use of corrugated surfaces can enhance flex and bending mechanical strength. For other installations, a smooth surface reduces the possibility of high friction when pulling cable into areas where it may contact surfaces other than the raceway or plenum. Mechanical integrity using an outer jacket such as depicted in FIGS. 2A, 2B, or 2C may be essential for installation purposes.
Alternatively, depending on manufacturing capabilities, the use of a tape or polymeric binding sheet may be necessary in lieu of extruded thermoplastic jacketing. Taping or other means may provide special properties of the cable construction such as reduced halogen content or cost and such a construction is found in FIG. 2C.
Yet another related embodiment includes the use of a strength member together with, but outside of the multi-anvil shaped core support-separator running parallel in the longitudinal direction along the length of the communications cable. In a related embodiment, the strength member could be the core support-separator itself, or in an additional related embodiment, the strength member could be inserted in the hollow center-portion of the core.
According to another embodiment of the invention, the multi-anvil shaped core support-separator optionally includes a slotted section allowing for insertion of an earthing wire to ensure proper and sufficient electrical grounding preventing electrical drift.
Finally, it is possible to leave the multi-anvil shaped separator cavities empty in that the separator itself or within a jacket would be pulled into place and left for future xe2x80x9cblown fiberxe2x80x9d or other conductors along the length using compressed air or similar techniques such as use of a pulling tape or the like
It is understood that each of the embodiments above could include a flame-retarded, smoke suppressant version and that each could include the use of recycled or reground thermoplastics in an amount up to 100%.
A method of producing the communications cable, introducing an anvil-shaped core as described above, into the cable assembly, is described as first passing a plurality of transmission media and a core through a first die which aligns the plurality of transmission media with surface features of the core and prevents or intentionally allows twisting motion of the core. Next, the method bunches the aligned plurality of transmission media and core using a second die which forces each of the plurality of the transmission media into contact with the surface features of the core which maintain a spatial relationship between each of plurality of transmission media. Finally, the bunched plurality of transmission media and core are optionally twisted to close the cable, and the closed cable optionally jacketed.